Owners keeping their cat's bowl topped up with dryfood may be causing them to gain weight.

Just like people, cats will overeat if they get the chance. New research into cat food suggests overindulgence in popular dry cat biscuits may be to blame for fuller feline figures.

The ease and convenience of dry cat biscuits heightens the risk of owners perpetually topping up the dish and overfeeding their pet, says researcher Dr David Thomas, director of the University’s Centre for Feline Nutrition in Palmerston North.

Dr Thomas says cats are naturally designed to eat several small, protein-packed meals a day.

The study, which set out to establish whether there is any link between dry food consumption and weight gain in cats, found that those fed solely on dry biscuits got plumper but lost weight once they changed to a wet, or canned food diet.

Sixteen adult cats bred at the centre and normally fed canned diets were split into two groups. After an initial period during which both groups were given just dry food, one group changed to canned meals and the other continued with dry biscuits. Those eating only dry food put on weight, while the group fed canned food lost weight.

But well-meaning cat-owners tended to feed them dry food on demand, rather than in accordance with any measured portions, Dr Thomas says.

He says cats were first domesticated by the ancient Egyptians to keep mice away from grain stores. They obtained most of the water needed for survival from eating fresh meat in a similar way to other desert carnivores.

But some of the modern dry food cat diets have been shown to result in lower water intakes. Dry food has around four times the energy content of canned food.

“Obesity levels in companion animals frequently mirror that of their owners.” Other studies have estimated that between 25 and 40 per cent of pets worldwide are overweight.

His findings will be presented at a major nutrition conference at the University's Auckland campus, which will be held on 5-7 December 2007.